Talk:Thermistor

From Wikipedia, the free encyclopedia

WikiProject Physics This article is within the scope of WikiProject Physics, which collaborates on articles related to physics.
??? This article has not yet received a rating on the assessment scale. [FAQ]
??? This article has not yet received an importance rating within physics.

Help with this template Please rate this article, and then leave comments to explain the ratings and/or to identify its strengths and weaknesses.
WikiProject on Electronics This article is part of WikiProject Electronics, an attempt to provide a standard approach to writing articles about electronics on Wikipedia. If you would like to participate, you can choose to edit the article attached to this page, or visit the project page, where you can join the project and see a list of open tasks.
B This article has been rated as B-Class on the quality scale.
Mid This article has been rated as Mid-importance on the importance scale.

Nice article. One question: "Many NTC thermistors are made from a thin coil of semiconducting material such as a sintered metal oxide. They work because raising the temperature of a semiconductor increases the number of electrons able to move about and carry charge - it promotes them into the conducting band". This is nice simple explanation for NTC, but how does PTC work then? Thanks! --User:Chinasaur

Contents

[edit] B-Constant

I've seen the b-constant specified on many datasheets for thermistors, yet can't find a good description of it. My understanding is that it is a way to approximate the R-T relationship that is much worse than the Steinhart-Hart equation? --User:Pigrew


[edit] Revisions

I removed this application:

  • Thermistors are used in smart camera flash guns which adjust for proper film exposure according to the light reflected.

Wow - it appears to have been in the article a long time. I think this is totally wrong because thermistors aren't light sensitive! The author must have been thinking photoresistor, but those are typically slower and used to determine exposure when no flash is used. I could also see them used in flash battery packs, but again, no light-sensing application.

[edit] Added B parameter equations

I added the B (beta) parameter equations. They are the ones used by engineers. Mircealutic 18:55, 21 December 2005 (UTC)

[edit] Picture

Trivial point but there must be a better picture of a thermistor out there. Also it may be an idea to get it put onto the page rather that linking to it. Wheatleya 22:11, 22 February 2006 (UTC)


[edit] NTC vs. PTC

Our physics laboratory tutor claims that all the thermistors are NTC type and in fact there are no such that of the coefficient positive. Or maybe it is just him who hasn't met them yet.

A combination of a ptc and an ntc thermistor have been used to control CRT degauss coils since the year dot.

Tabby (talk) 23:39, 11 January 2008 (UTC)

[edit] B-parameter equations

The first B-parameter equation is incorrect. It is algebraically inconsistent with the second B-parameter equation, which is correct. The first equation should be... 1/T = 1/T0 + ln(R/R0)/B. Please note also that T0 in these formulas is Kelvin temperature, while the last part of the B-parameter addition says "R0 is the resistance at temperature T0 (usually 25C)". It should say "T0 (usually 298.15K)". That's the same temperature, of course, but if 25 is used in the equations as T0, they won't work. -- John O'Flaherty

Hopefully they are fixed, but please check. PAR 17:56, 2 August 2006 (UTC)
It looks right, now. Also added parentheses around the denom. in eqn.4 of that section. J.O'F,8-5-2006.

[edit] Steinhart-Hart parameters for 3 KOhms Thermistor

A very nice article. Thank you!

However I think there is a mistake: Using the parameters you give for a 3 KOhms thermistor

a = 1,40E-03 b = 2,37E-04 c = 9,90E-08

at 25°C (= 298.15 K) I get a resistance of 5264,260842 Ohms. The expected value of 3000 Ohms I get at 35.9906°C. Is there an error in the parameters?

Another question: Can you please publish the parameters for most common thermistors (like 30K, 100K), or help me where I can find them?

Email: m31415@nurfuerspam.de

Thanks,

Martin

I don't know what you did wrong but when I use:
R=e^{{\left( \beta-{\alpha \over 2} \right)}^{1\over 3}-{\left( \beta+{\alpha \over 2} \right)}^{1\over 3}}
with T=298.15, I get 3067.5 ohms, which is off by about 2 percent, which is about the roundoff error in the abc coefficients. If you still get a different answer, list all your steps and values, so we can find the error. Theres a lot of good information at the at the YSI technical page PAR 15:22, 7 August 2006 (UTC)

[edit] R is wrong

Equation of R in function of T is wrong!

[edit] Suggested merge with Resistance thermometer

NO MERGE - these are two entirely different devices and should not be confused. PAR 16:08, 1 February 2007 (UTC)